Resin-impregnated leather board



Patented June 2 1, 1952 2,601,671 r RESIN-IMPREGNATED LEATHER BOARD Lucius H. Wilson, Greenwich, Chester G. Landes,

New Canaan, and Charles S. Maxwe l, 01d

Greenwich, Conn., assignors to American Cyanamid'Company, New York, N. Y'., a, corporation of Maine No Drawing. Application October 23; 1946, ScrialNo. 705,242

. 1 This invention relates, provedphysical, characteristics and to, method for; its manufacture. Afprincipal object is the provision of leather board of improvedmechanical and, tensile strength and Wet-rub resistance, prepared by impregnating leather fibers with resinous, materials followed by forming the impregnatedfleather fibersinto a waterlaid product.

For many years it has been, commercial prac-, ticeto, utilize scrap, leather such as trimmings from shoe manufacture and also waste leather from Worn-out leather products, etc.by shredding, grinding or otherwise converting it into leather fibers which are suspended in water and formed into a waterlaid or molded product, known as leather board, It has also been proposed to incorporate waxes such as, parafiinwamsoaps, rosin andother organic materials into the leather fiber suspensions prior to the forming step in order to improve the Water resistance of the leather board. The present invention provides an improvedmethod ofincorporating-such organic materials into the leather fibers and also includes, among its more specific features, the incorporation ofthermoplastic and thermosetting" resins such as polystyrene, polyethylacrylate, phenolformaldehyde resins and the like.

Our present invention isbased on the discovery of an unusual type of flocculation and deposition that is brought about by the action of colloidal cationic melamine-aldehyde resins in an aqueous system containing leather fibers suspended there in together with an aqueous dispersion of waterinsoluble coating or impregnating agents of the type referred to above. It has been found that in such a system the cationic melamine-aldehyde resin causes a controlled flocculation such that particles of the impregnating agent are uniformly coated upon or impregnated into the leather fibers. When dispersed or deflocculated waterinsoluble impregnating' or coating agents are applied." in this manner the leather fibers retain their property of felting or forming into shaped or sheeted articles. despite the presence of substantial quantities of the impregnating agent. Moreover, a high degree of retention of the flocculated material by the leather fibers is obtained, and: losses of organic material in the white water system are largelyavoided.

The process of our invention therefore comprices as an essential feature the flocculation of an aqueous dispersion of a water-insoluble organic impregnating agent in the presence of leather fibers, suspended in an aqueous medium, thisflocculation being brought about by the action; of a cationic, melamine-aldehyde condensa- 2 Claims. (01. 92 521) to, leather board of im tion product such as cationic melamine-formaldehyde resin. The invention in its broader aspects includes any process wherein this fiocculating action is used for the deposition or incorporation of' an organic impregnating agent into leather fibers. One of its most important features is the discovery that the distinctive flocculating action of the cationic melamine-aldehyde resin continues, and is in many cases actually enhanced, after the cationic resin has been adsorbed on the leather fibers, The importance of this discovery resides in the fact that the cationic resin, being distributed uniformly over and through the leather fibers, causesfa uniform deposition and retention of the impregnating agent on the leather fibers after it has been nee culated. The felting and sheet-forming properties of the fibers are therefore retained eventhough they may contain large quantities of the organic impregnating agent, and the aqueous fiber suspension, afterthe resin addition, can be formed into sheeted or molded products by conventional wet-molding or papermaking procedures. p The flocculating agents which we employ in practicing our invention, and which are designated as "cationic melamine-aldehyde resins, are resinous materials containing melamine and carrying a positive electrical charge when in aqueous solution. These colloidal resin solu-. tions may be prepared by dissolving ordinary melamine-aldehyde condensation products, such as methylol melamines, in acids such as hydrochloric acid to form acidified or acid-type resin solutions having a glass electrode pH valve within the range of about 0.5 to about 4 when measured at 15% solids, or pH values up to about 4.5, when measured in more dilute solutions, followed by aging to the colloidal condition, as described in U. S. Patent No. 2,345,543. p 7

Any water-insoluble coating or impregnating agent may be applied by the process of our invention in amounts varying from a few per cent up to more than theweight of the leather fibers. By coating or impregnating agent we mean a material which will coat or impregnate the leather fibers and improve their value for their intended use in the production of leather board. Most of the coating or impregnating agents used in practicing the invention are organic amorphous, or micro-crystalline materials of the type of waxes, gums, resins and the like such as micro-crystalline or amorphous petroleum waxes, bituminous materials such as tars and pitches, wood rosin or gum rosin, hydrogenated rosin, elastomers such as natural or synthetic laticespolymers.

of butadiene, isoprene etc. and their copolymers with acrylonitrile; thermosetting resins such as alkylated or alcohol-reacted urea-formaldehyde resins, phenol-aldehyde resins, etc. and thermoplastic resins such as polyvinyl compounds, poly styrenes, polyacrylates, polymethacrylates, polyvinyl esters such as Vinyl chloride and vinyl acetate polymers, coumarone and indene resins, esters of rosin with glycerine and other polyhydric alcohols and the like. 1

The leather fibers with which the above impregnating agents are incorporated may be obtained from any suitable source, and include leather tanned by any suitable procedure. Vegetable tanned leather, chrome tanned leather,

alum tanned leather, as well as leather prepared.

by aldehyde tannages, aromatic sulfonic acid tannages, iron tannages and the like may be used,

either singly or in admixture. The stock may consist entirely of leather fibers or may be a major proportion thereof, it may be admixed with other fibers such as various cellulosic fibers including kraft paper stock, rag stock, sulfate, ground-wood or sulfite stock or other forms of fibrous cellulose such as hydrated cotton linters, jute, hemp. sisal, strings, chopped canvas, etc. Similarly, mineral fibers such as asbestos fibers or glass fibers may be incorporated if desired. This stockmay be used as such, or it may be pretreated with rosin size, wax size or other common sizingagents and alum in the usual manner. The organic impregnating agents such as those listedabove, either singly or in admixture, are added to the aqueous stock suspension containing the leather fibers as a dispersion in water or aqueous liquid. Depending on the type of impregnating agent, the dispersions may require no added emulsifying or dispersing agents whatsoever, as in the case of natural latices. However, in many cases dispersions of finer particle size and better impregnating properties are obtained with the aid of dispersing agents, and many types of dispersing agents may beused. In general, any anionic or non-ionic dispersing agent may be employed in emulsifying or suspending the impregnating agents in water or other aqueous liquids, and in certain cases the cationic emulsifying agents may also be used. Typical anionic emulsifying agents that may be employed are the soaps of aliphatic and cycloaliphatic acids such as potassium oleate and potassium naphthenate, amine soaps such as triethylamine laurate, triethanolamine oleate and 'sulfated or sulfonated compounds such as sodium lauryl sulfate, sodium keryl benzene sulfonate, sodium isopropyl naphthalene sulfonate, esters of sulfocarboxylic acids such as sodium dioctylsulfosuccinate, sulfonated lignin and the like. Typical non-ionic emulsifying agents are polyhydric alcohol esters such as polyethylene glycol-substituted maleic acid esters, mannitan and sorbitan monoesters of palmitic, stearic or oleic acids or their ethylene oxide condensation products, and ethylene oxide condensation products of lauryl or tetradecyl or oleyl alcohols. Gums and proteins may also be used as emulsifying agents or as emulsion stabilizers such, for example, as gum arabic, soya bean protein, ammonium caseinate and the like.

The particular procedure whereby the impregnating agent is fiocculated and coated on the leather fibers, or on {mixed stock containing leather fibers, may vary somewhat with different impregnating agents but usually follows the same general plan. The leather is shredded or ground or otherwise reduced to a finely divided, fibrous condition and may be washed and beaten in Water if necessary to liberate undesired impurities and refine itto the condition necessary for treatment, and sizing agents may be added if desired. The stock is then suspended in suflicient -water to dilute it to a consistency of about '0.5-6%, consistencies of 1-2% being preferred,

' dehyde for each mol of melamine by dissolving it in about 0.8 mols of dilute hydrochloric acid for each mol of melamine and adding Water at 60- 80 F. to make a resin solids content of 10-15%. This solution is allowed to age at ordinary temperatures for about 3-10 hours, preferably overnight, whereupon it is converted into a colloidal cationic melamine-formaldehyde resin solution. After adding the desired amount of this resin solution to the aqueous stock suspension the mixture is preferably allowed to stand for a period of time from about 15 minutes up to 3-4 hours or longer, after which an aqueous dispersion of the impregnating agent is added with agitation to insure a uniform mixture and the treated stock is run off on a papermaking machine or molded into the desired shape on a wet-molding machine. The amount of impregnating agent may vary from 1-2% up to 100% of the weight of the fibers, quantities of 15-40% being suitable for most purposes.

The amount of the colloidal cationic melamine-aldehyde resin solution to be used may also vary Widely, since leather fibers will adsorb up to 50% of their weight of the cationic melamine resin. However, for most purposes it is unnecessary to use large amounts of this resin; experiments have shown that about 145%, based on the Weight of the fibers to be impregnated (including the weight of the vegetable or mineral fibers if any) is suificient for most practical purposes. These quantities of the cationic melamine resin will effect the flocculation and retention of much larger quantities of deflocculated organic impregnating agents, such as those outlined above, and will bring about a uniform deposition of these impregnating agents upon the fibers of the stock including particularly the leather fibers.

The reason for aging the stock suspension for 0.253 hours or longer after adding the colloidal melamine resin solution is to improve the drainage of the stock on the forming wire or screen.

13y allowing the suspension to stand for this period of time before adding the impregnating agent the drainage time of the treated stock is materially reduced, so that the forming or mold ing operation can be carried on at a higher rate. The drainage characteristics of the stock are also improved by the acid present in the colloidal melamine resin solution; experience has shown that when the stock is neutral or alkaline it is much slower in character than when it is acid, and for most purposes a pH of from slightly below 4.0 to about 5 will be found to give the best results.

Although a high degree of flocculation and retention of the added impregnating agent is obtained by the use of cationic melamine-aldehyde resins, as described above, it is sometimes advantageous to add an additional precipitating agent during the stock preparation. Thus, for example, small quantities of aluminum sulfate on the order of 0 .5-3% may be added, as an assistseer-.011

5'.- ant in controlling ream; sticking" the press rollsother dimculties' imsheet manufacture; oi1 fbr"purpbses of pH control; The alum is almuster-ways? added after ther other ingredients have been-mixed,.sinceitiwom'datend to calculate aria precipitate the other. materials if it=were added first? The stock,.after pretreatmeh .with the. cau tic melamine resiii and the-- impress natingage may also be giveman atten-treatwith izes, pigments;coloring;materlals andi the like if desi'red.

I The invention willbe furtherilliistratelfby tlre frilldwiiig specific examples; .Itwshould beundera tanned ieatiier; were washed andsuspen ed in water and dilutedlib cdh'sl s t eilcy' 5f" 1.5%" bind a colloidal cationic melamine-formaldehyderesin, prese s previou' desbiib'edi was added ih amouiitse thesurpension wasadjiisted to weasellowed to stand for 30 minutes after which a pol'y styrene emulsion was added with agitation inan uwawnttomcf theineiaminares in on the dry weight of the fiber. of

Example 3.; A. pciyetnymcryiataemulsion was prepared by heatingfafsoliitibn ofEpartS-ofsodium l'auiy1' sulratein 14'spartsorwat'er to 90" c1, dissoiv ngzsparts of 30% hydrogen peroxide therein, andthen:

adding 100 parts or ethyl'acrylate monomer slow-"- 1ywith continuous agitation; The mixture was maintained at 90G. for one hour, afterwhich' time thepolymerizatibn was complete; and" any: small: quantities of monomerthat remained were removedbysteam-distillation. 'I'lie emulsion was then adjiusted' to 2'5' resin solid.

Fibers of vegetable tanned scra lea-therweresu'spefided in" water at 1.5% c'onsistency'and "the suspension.wasdividediinto a number'o'fportions. Tb three these rti'ons 'acolloidalcationic melamineforinaldehyde resimsoiution was added; th'epH'was adiii'stedi 1501410;.andtheywereiallowed restate-cots hours. To another: portion. 3%; of alum added. amcurrts ortne above poly ethyla'c late emulsion were then: added tdtwo or tnesuspensi'ons; one pref;mated withxmelamine resin and the other with alum, and all the samples; weremade-i'ntc leather board by the procedure de'scr'ibed in Example 1 and dried at 130 h. The boards were tested for tensile strength; dimensional stability; water absorption, wet-rub resistance- 'and tearing resistance; the results being Q givenln 'the following: table:

amount sufilcient to provide 40% of polystyrene resin, based on the dry weight of the leather adjustedfto solids. Duponol C is a higher alkyl sulfate (molecular weight 350) containing 10.8% NazSOi and 3.4% moisture.

The stock was made into board on a handsheet maehine by diluting to 1% fiber consistency' and' drawing-the; suspension onto the papermaking wire with the aid of a vacuum. The sheets were pressed to remove excess water and then dried by heatingin a laboratory oven at 100-160 F. i The white water from the sheetmaking wire was clear, showing that substantially all of the polystyrene had been'flocculated and retained.

' Example 2 A wax emulsion was prepared by adding 225 parts by weight of molten scale wax and 22 parts of oleic acid to 250 parts of hot water containing 2.6 parts ofNaOH followed by heating for 15 minutesJand homogenizing to a smooth emulsion of 1-2microns particle size.

A portion of the leather fiber suspension o Example 1, having a consistency of 1%, was pretreated with 2% of the cationic melamine-formaldehydefresin, based on the dry weight oithe leatherfriber, allowed to stand minutes, and sufficient of the above-described wax emulsion was added to incorporate 15% of wax, based on the weight lot the leather fiber. The mixture was agitated until flocculation was complete and was then madeinto leather board by the procedure described in Example 1. The wax was impregnated uniformly throughout the leather board, which had a high degree of water resistance and improved flexibility and softness.

reaction proceeded Steam was blown through the batch to remove unpolymerized material and the dispersion was Sample No 1' 2 i 3 4 5 Melamine Resin, percent 0 0i 3: 3 1.0 Polyacrylate Resin, percent... 0 30 30 0 0 Alum, percent 0 3 0 0 0 Basis Weight, lbs. (25 i0500). 159. 8 204 215. 5 186. 7 201. 5 Caliper (inchesXl000) 19.4 18.1 19.1 20. 4 20.0 Tensile Strength, lbs/inch:

Dry 1.76 12. 36 18. 32 8.2 13.0 et 0.4 4.6 8.2 1.6 3.4 Elongation, percent:

Dry 2.1 19.6 17.6 1.8 2.0 Wet 5-8 31 33.5 3.0 3.2 Initial Tear, g 0 656 803 280 435 Elmendor! Tear, g 43. 2 255. 2 264 128 176 Wet Rub, Taber Cycles 2 79 130 6 88 Water Absorption, percent..... 126 72 54 108 90 A comparison of the tabulated results shows that the fiber pretreated with the cationic melamine-aldehyde resin and then with the polyacrylate emulsion produces leather board of greatly improved characteristics, as compared with the fiber pretreated with alum. The tensile strength of the melamine resin-pretreated board is greatly improved, as is also the wet-rub resistance and tearing resistance and the water absorption i considerably reduced.

Example 4 A 15.% water suspension of the leather fiber described in Example 3 was treated with 3% of colloidal cationic melamine-formaldehyde resin and divided into several portions which were adjusted to varying degrees of acidity by the addition of hydrochloric acid or sodium hydroxide. The suspensions were then allowed to stand 3 hours, 30% of the polyethylacrylate emulsion of Example 3 was added, and the stock was made into leather board in a laboratory handsheet machine provided with a calibrated glass cylinder so that the rate of drainage through the wire could be measured. The drainage of stock adjusted to a pH of 3.2 was 13 seconds; that of stock having a pH of 4.0 was seconds; when the pH was 4.9 the drainage time was seconds, and at pH 6.1 it was seconds. These figures emphasize the desirability of maintaining a low pH during the time when the stock suspension is allowed to stand before adding the impregnating agent.

What We claim is:

1. Ina method of making leather board by the steps of preparing an aqueous suspension of 11- brous sheet-forming material including a major proportion of leather fibers, impregnating the fibrous material with a water-insoluble hydrophobic organic impregnating agent and forming the impregnated fibrous material into a felted product, the improvement which consists in first adding to the aqueous fiber suspension 1-15% of melamine resin, based on the dry weight of said fibrous material, in the form of a colloidal solution of cationic hydrophilic melamine-formaldehyde resin, then aging the suspension for at least ,30 minutes, then adding an aqueous dispersion of the water-insoluble hydrophobic organic impregnating agent in deflocculated condition and flocculating the impregnating agent in the presence of the suspended fibers by the action of the cationic melamine resin, and thereby depositing the impregnating agent uniformly on the fibers along with melamine-formaldehyd resin.

2. A method according to claim 1 in which the water-insoluble hydrophobic impregnating agent is a polyethylacrylate resin.

LUCIUS H. WILSON. CHESTER G. LANDES. CHARLES S. MAXWELL.

REFERENCES CITED UNITED STATES E Dateif' t Number Name 1 1,777,838 Ferretti Oct;-7, 1930 1,992,589 Tucker Feb. 26, 1935 2,040,511 Bleyenheuft et al. May 12, 1936 2,140,932 Avery Dec. 20, 1938 2,237,235 Lynam Apr.- 1, 1941 2,315,675 TrommsdoriT Apr. 6, 1943 2,343,095 Smith L' Feb. '29, 1944 2,363,439 Richter Nov. 21, 1944 2,394,009 Pollard Feb. 5, 1946 2,401,027 Tausch May 28, 1946 2,488,515 Sherman et-al.-" Nov. 15, 1949 2,492,702 N'eubert et' al. Dec; 27, 1949 2,563,897 i Wilson et al. Aug. 14, 1951 j FOREIGN PATENTS p Number Country .Date' 511,865 Great Britain Aug. 25, 1939 OTHER REFERENCES 

1. IN A METHOD OF MAKING LEATHER BOARD BY THE STEPS OF PREPARING AN AQUEOUS SUSPENSION OF FIBROUS SHEET-FORMING MATERIAL INCLUDING A MAJOR PROPORTION OF LEATHER FIBERS, IMPREGNATING THE FIBROUS MATERIAL WITH A WATER-INSOLUBLE HYDROPHOBIC ORGANIC IMPREGNATING AGENT AND FORMING THE IMPREGNATED FIBROUS MATERIAL INTO A FELTED PRODUCT, THE IMPROVEMENT WHICH CONSISTS IN FIRST ADDING TO THE AQUEOUS FIBER SUSPENSION 1-15% OF MELAMINE RESIN, BASED ON THE DRY WEIGHT OF SAID FIBROUS MATERIAL, IN THE FORM OF A COLLOIDAL SOLUTION OF CATIONIC HYDROPHILIC MELAMINE -FORMALDEHYDE RESIN, THEN AGING THE SUSPENSION FOR AT LEAST 30 MINUTES, THEN ADDING AN AQUEOUS DISPERSION OF THE WATER-INSOLUBLE HYDROPHOBIC ORGANIC IMPREGNATING AGENT IN DEFLOCCULATED CONDITION AND FLOCCULATING THE IMPREGNATING AGENT IN THE PRESENCE OF THE SUSPENDED FIBERS BY THE ACTION OF THE CATIONIC MELAMINE RESIN, AND THEREBY DEPOSITING THE IMPREGNATING AGENT UNIFORMLY ON THE FIBERS ALONG WITH MELAMINE-FORMALDEHYDE RESIN. 